Electrical properties of hydrated collagen. I. Dielectric properties

The effect of water on the low-frequency (10²-10⁵ H_z) complex permittivitv of native, sold-state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is absorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary absorption layer as determined from independent water absorption studies. The behaviour is qualitatively identical to that observed for other proteins and related materials. Temperature-dependent measurements made under vacuum conditions in the range ?196°C to +100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperature-dependent curves is found at about +40°C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to free states, and (2) the difffusion of water molecules out of the system. The dielectric constant of dry collagen, after desorption at ambient temperature, is about 4.5. Desorption at elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from the optical value of n² = 2.16.     

Methods for syntheses of <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">DL</Emphasis>-aspartic acid derivatives

Summary. A novel practical method for the synthesis of N-methyl-DL-aspartic acid 1 (NMA) and new syntheses for N-methyl-aspartic acid derivatives are described. NMA 1, the natural amino acid was synthesized by Michael addition of methylamine to dimethyl fumarate 5. Fumaric or maleic acid mono-ester and -amide were regioselectively transformed into beta-substituted aspartic acid derivatives. In the cases of maleamic 11a or fumaramic esters 11b, the α-amide derivative 13 was formed, but hydrolysis of the product provided N-methyl-DL-asparagine 9 via base catalyzed ring closure to DL-α-methylamino-succinimide 4, followed by selective ring opening. Efficient methods were developed for the preparation of NMA-α-amide 13 from unprotected NMA via sulphinamide anhydride 15 and aspartic anhydride 3 intermediate products. NMA diamide 16 was prepared from NMA dimethyl ester 6 and methylamino-succinimide 4 by ammonolysis. Temperature-dependent side reactions of methylamino-succinimide 4 led to diazocinone 18, resulted from self-condensation of methylamino-succinimide via nucleophyl ring opening and the subsequent ring-transformation.     

Chiral chemical absorption property of a cross-linked poly(N-isopropyl acrylamide-co-sodium acrylate) thermoresponsive smart gel

This investigation leads to the chiral chemical absorption property of a thermoresponsive gel material. d ‐(+)‐α‐phenyl ethyl amine was taken as the chiral chemical. The gel material was synthesized by polymerizing 1:1 mole ratio of N‐isopropyl acrylamide and Na‐acrylate along with methylene bisacrylamide (2 wt.% of total monomer) as a cross‐linker using ammonium persulfate as an initiator and N, N, N′, N′‐tetra‐methyl ethylene diamine as an accelerator. The microporous nature of the gel material is observed by scanning electron microscope as well as by surface analysis. It is a pH as well as thermoresponsive gel. The highest gel swelling is observed at around pH 8.2 at room temperature (30 °C). The gel contains carboxylate (―COO^?) group in this slightly alkaline condition. In the ionic state, the mutual repulsion of the ionic groups helps in swelling the gel. The lower critical solution temperature (LCST) of the gel is observed to be about 38 °C, which is higher than that of poly N‐isopropyl acrylamide itself (32 °C). This corroborates with the theory and other reported results that LCST increases with the incorporation of ionic moiety in the cross‐linked copolymer. The chiral chemical absorption of the gel material was monitored by measuring circular dichroism of the chiral compound in the presence and absence of gel using a circular dichroism spectropolarimeter (J‐810 L) (JASCO International Co., Ltd., Tokyo, Japan). About 18% of d ‐(+)‐α‐phenyl ethyl amine is absorbed from its aqueous solution by 0.01 g of dry gel material (particle size: 106–212 µm) at room temperature. The absorption of the chiral compound is reversible with temperature having a sudden jump at LCST (38 °C) of the gel material. Chirality 24:506–511, 2012. © 2012 Wiley Periodicals, Inc.     

A Tunable Ultra-Broadband Metamaterial Absorber with Multilayered Structure

In this article, we demonstrate a tunable ultra-broadband metamaterial absorber (TUMA) in terahertz (THz) band which is based on the multilayered structure composed of an Au reflective layer, polyimide dielectric layers, and vanadium dioxide (VO₂) periodic structures, respectively. We gain the tunable absorption spectra because of the room temperature phased-changed character of VO2. The relative bandwidth reaches to 81.2% and the absorption rate is over 90% at the frequency range of 1.63–3.86 THz when the temperature (t₁) is 350 K, but when t₁ = 300 K, the presented absorber is acted as a reflector whose absorption is small besides the frequency points of 9.75 THz and 9.81 THz. For the sake of comprehending the physical mechanism in-depth, the electric field (E-field) diagrams, the surface current distributions and the power loss density (PLD) of the TUMA are investigated. The influences of structural arguments and incident angle (θ) on the absorption are also analyzed. The emulated consequences show that the absorption spectrum can be regulated by changing structural parameters and incident angle and the tunable absorption regions can be obtained by altering the external temperature.

     

Solvent effects of N‐nitroso,N‐(2‐chloroethyl), N′,N′‐dibenzylsulfamid and its copper(II) and cobalt(II) complexes: fluorescence studies

The structure of N‐nitroso, N‐(2‐chloroethyl), N′,N′‐dibenzylsulfamid (CENS) was established by X‐ray crystallography. The atomic coordinates, factors of isotropic thermal agitation, bond lengths and valence angles were determined. The solvent effects on the electronic absorption and fluorescence spectra of CENS were investigated at room temperature. The effects of solvent polarity and of hydrogen bonding were interpreted by means of linear solvation energy relationships (LSERs). Multiple linear regression analysis indicated that the hydrogen donation properties of the solvent play an important role in determining the position of the absorption maximum, while the classical polarity of the medium is the only dominating parameter in determining the emission maximum and the Stokes' shift. Complexation of the investigated compound by two different transition metal ions was studied. Fluorescence measurements show that fluorescence quenching by cobalt(II) is more important than that by copper(II). This phenomenon can be attributed to good stereo‐structural matching between the electronic configuration of the Co²⁺ ion and the active site distribution of CENS in aqueous solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Monoalkyl phosphodiesters: Synthesis and dielectric relaxation of solutions

Chromatographically pure hexadecylphosphocholine, -(N,N-dimethyl)-ethanolamine, -(N-N-methyl)-ethanolamine and -ethanolamine have been synthesized. Aqueous solutions of these phospholipids have been prepared for the purpose of measuring their dielectric spectra. Micellar solutions appropriate for the dielectric studies were obtained with the choline and the (N,N-dimethyl)-ethanolamine head groups.The dielectric spectra of these phospholipid/water systems are evaluated in terms of phenomenologically introduced sum of Cole-Cole relaxation functions and also on the basis of a model relaxation function which has regard to internal depolarizing fields of the colloidal solutions. Parameters reflecting the motions of the dipolar head groups and of the hydration water molecules of the synthetic monoalkyl phosphodiesters are discussed and are compared with those for egg lysolecithin.The mobility of the dipolar phospholipid head groups and the number of influenced water molecules per zwitterion decreases when changing from lysolecithin to hexadecylphosphocholine and further to hexadecylphospho-(N,N-dimethyl)-ethanolamine, while the relaxation time of the hydration water increases. These results indicate the micellar surface to get less porous within the above series of lipids.     

Dielectric relaxation of DNA solutions. II

Real and imaganiry parts of complex dielectric constant of dilute solutions of DNA in 10^?3M NaCl with molecular weight ranging from 0.4 × 10⁶ to 4 × 10⁶ were measured at frequencies from 0.2 Hz to 30 kHz. Dielectric increments Δε were obtained from Cole-Cole plots and relaxation times τ_D from the loss maximum frequency. The τ_D of all samples agrees well with twice of the maximum viscoelastic relexation time in the Zimm theory, indicating that the low-frequency dielectric relaxiation should be ascribed to be the rotation of DNA. The rms dipole moment, which was obtained from Δε, agree well with that calculated from the counterion fluctuation theory. The dielectric increment was found to be greatly depressed in MgCl₂, which is resonably interpreted in terms of a strong binding of Mg⁺⁺ ions with DNA.     

Relaxation processes on a picosecond time scale in hemoglobin and poly(L-alanine) observed by millimeter-wave spectroscopy

Broadband measurements of the millimeter-wave and far-ir absorption (10–10⁴ GHz) of lyophilized hemoglobin are reported. Additionally, the absorption of poly(L -alanine) and crystalline L -alanine at 70 GHz was measured for comparison. All measurements were extended over the temperature range from liquid helium to room temperature. For the millimeter range, this was attained by using the novel oversized-cavity technique. It was found that the millimeter-wave absorption of the materials increased nearly exponentially with temperature and increased as ν^1.2–ν² with frequency. The far-ir absorption of hemoglobin showed broadbands with almost no temperature dependence. The frequency and temperature dependence of the millimeter-wave absorption is quantitatively described as due to three distinct relaxation processes on a picosecond time scale occurring in asymmetric double-well potentials. These processes are most probably assigned to the NH ?OC hydrogen bonds of the peptide backbone.     

Effect of salt on the stability of the pH 4.2 rA8 double helix in a series of organic/aqueous mixed solvents: A test of oligoelectrolyte theory

Temperature-dependent uv absorption spectroscopy has been used to investigate the salt dependence of the order–disorder transition for the pH 4.2 rA₈ double helix in 100% aqueous buffer and in a series of organic/aqueous mixed solvents. Melting temperature, T_m, data were obtained for the transitions in the different solvents by analysis of the uv melting curves. For the pure aqueous buffer solvent, the melting temperature was found to exhibit a reduced salt dependence (?t_m/? log Na⁺) when compared to the corresponding polymer. This reduction is explained in terms of end effects and is shown to be consistent with the theoretical treatments of oligoelectrolyte transitions developed by Record and Lohman [Biopolymers, 17 , 159–166 (1978)]. In the mixed solvents, the salt dependence of the melting temperature (?t_m/? log Na⁺) is shown to exhibit a linear dependence on the bulk dielectric constant of the medium for all of the hydroxyl-containing solvents studied. Significantly, N,N-dimethylformamide demonstrated different behavior.     

Spatial and temporal variations in the photosynthesis-nitrogen relationship in a Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) canopy

Spatial and temporal variations in light-saturated photosynthetic capacity and needle nitrogen (N) content were investigated in one 8 m tall Japanese cedar (Cryptomeria japonica D. Don) canopy for a full year. The photosynthetic capacity and needle N content in various layers of the canopy were measured every month. Temporal variations in photosynthetic capacity and needle N content expressed on a projected-area basis (P_area, N_area) were similar. Furthermore, both P_area and N_area decreased with increasing depth from the top of the canopy on each sampling date. As a consequence, a significant correlation was observed between N_area and P_area. Temporal variations in photosynthetic capacity and needle N content expressed on a mass basis (P_mass, N_mass) were also similar. P_mass also decreased with increasing canopy depth. However, in contrast to N_area, there was only a slight decrease in N_mass with increasing canopy depth. Hence, the correlation between N_mass and P_mass was lower than the projected-area value. Because N_area was highly correlated with the needle mass per projected-area (NMA), the spatial variation in N_area (and therefore P_area) in the canopy is attributed to the variation in NMA, which decreases as the depth from the top of the canopy increases. Furthermore, the slope of the linear regression between N_area and NMA differed between sampling dates, indicating that the temporal variations in N_area (and therefore P_area) are strongly influenced by N_mass. For most of the sampling dates, a linear regression between N_area and P_area tends to converge into a single line segment. However, on several sampling dates, there was a pronounced decline in P_area below this line segment. This reduction in P_area, which does not accompany a reduction in Narea, seems to be attributable to stomatal limitations induced by the low soil temperature in winter and early spring.     

Dielectric relaxation of DNA solutions. IV. Effects of salts and dyes

The effects of salts (NaCl, LiCl, Me₄NCl, AgNO₃, MgCl₂, CuCl₂ and MnCl₂) and dyes (acridine orange and methylene blue) on the low-frequency dielectric relaxation (0.1 Hz–30 kHz) of dilute aqueous solutions of DNA were investigated with varying salt or dye concentrations. Both the dielectric relaxation time τ_D and the rotational relaxation time τ estimated from the reduced viscosity decrease in quite parallel ways with increasing M/P (M/P being the normality ratio of cation to phosphate residue), reflecting the contraction of DNA molecule due to electrostatic shielding and cation binding. The agreement between τ_D and τ through the whole range of M/P supports our previous conclusion that the low-frequency relaxation of DNA arises from rotation of the molecule. The dielectric increment Δε also decreases with increasing M/P on account of both the contraction of DNA and the decrease in effective degree of dissociation of DNA. Δε as a function of M/P is interpreted in terms of a quasi-permanent dipole due to counterion fluctuation. These effects of cations are the strongest for divalent cations and rather weak for Na⁺, Li⁺, and Me₄N⁺. Effects of dye on τ_D and Δε are also well explained by the rotation of DNA molecule with a quasi-permanent dipole due to counterion fluctuation on the basis of intercalation of dye at D/P < 0.2 (D/P being the molarity ratio of dye to phosphate residue) and external binding at 0.2 < D/P < 1.0.     

Power law dispersion in animal horn

The dielectric response of sheep horn has been measured in the frequency range from 10^–3–10⁵ Hz and over temperatures in the range 304–500 K. The dynamic behaviour of the conductance and capacitance in sheep horn has been observed to follow fractional power law dependences on frequency. It is shown that the over all dielectric response of these dead cells correspond to a dispersive imperfect bulk in series with a dispersive barrier region. It is further shown that the increase in temperature influences the reponse by eliminating the room temperature dc conductance and affecting the magnitude of the dispersion in capacitance. The magnitudes of activation energies are found as 0.33±0.02 eV for conductance, 0.40±0.02 eV for relaxation and 0.33±0.02 eV for the frequency shift.     

Dielectric relaxation of DNA in aqueous solutions.

Using a four-electrode cell and a new electronic system for direct detection of the frequency differences specturm of solution impedance, the complex dielectric constant of calf thymus DNA (M_r = 4 × 10⁶) in aqueous NaCl at 10°C is measured at frequencies ranging from 0.2 Hz to 30 kHz. The DNA concentrations are C_p = 0.01% and 0.05%, and the NaCl concentrations are varied from C_s = 10^?4 M to 10^?3 M. A single relaxation regions is found in this frequency range, the relaxation frequency being 10 Hz at C_p = 0.01% and C_s = 10^?3 M. At C_p = 0.05% it is evidenced that the DNA chains have appreciable intermolecular interactions. The dielectric relaxaton time τ_d at C_p = 0.01% agrees well with the rotational relaxation time estimated from the reduced visocisty on the assumption that the DNA is not representable as a rigid rod but a coiled chain. It is concluded that the dielectric relaxiatioinis ascribed to the rotation of the molecule. Observed values of dielectric increment and other experimental findings are reasonably explained by assuming that the dipole moment of DNA results from the slow counterion fluctuation which has a longer relaxation time than τ_d.     

Rheological Studies of Wheat Flour Dough

Dynamic rigidity G′, dynamic viscosity η′ and the relaxation spectrum L(t) of dough under periodic shear stress have been obtained. At first, G′ and η′ decreased rapidly with rest time, but maintained a constant value after 60 minutes. Values of both G′ and η′ decreased, and L(t) became flat with the decrease in water absorption and with the temperature. G′ increased slightly with the increase in salt content, but η′ decreased in a low frequency range.     

The dynamics of the DNA hydration shell at gigahertz frequencies

We have used Brillouin scattering to measure the linewidths and frequencies of GHz acoustic phonons in Na- and Li-DNA films as a function of temperature between 300 and 140 K for samples that were dry, lightly, and heavily hydrated. The linewidths decrease with falling temperature and water contents, indicating that coupling to a water relaxation is the main source of phonon damping. The strength of the relaxation was determined using measurements of the phonon linewidth as a function of frequency, and confirmed by comparison of measured and calculated spectral profiles. The relaxation strength is anisotropic, being greater for phonons propagating perpendicular to the helix axis. The hydrated DNA exhibits both a rapid relaxation (≤ 10^?11 s per radian) giving rise to a classical f² damping, and a slower motion with a relaxation time that varies from ～ 4 × 10^?11 s per radian (primary hydration shell) to ～ 2 × 10^?12 s per radian (secondary hydration shell) at room temperature. In the frequency interval that bounds these relaxation times (～ 4 to 80 GHz) we expect degrees of freedom associated with the primary hydration shell to be important. The sample with primary hydration follows a simple Arrhenius behavior with ΔH ～ 5 kcal mole^?1. The effective activation energy for the sample with secondary hydration is somewhat higher (indicating a more cooperative water relaxation) and varies strongly with temperature. The elastic moduli change much more than can be accounted for by relaxation, indicating the importance of water motion in softening interatomic potentials. The extent of the softening caused by the “unfreezing” of water motion is similar to the degree of softening caused by hydrating the sample.     

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium <Emphasis Type="Italic">Thermochromatium tepidum</Emphasis>

The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N = 11) and spirilloxanthin (N = 13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N = 13) to play the role of the direct quencher of the excited singlet state of BChl.     

Broadband dielectric spectroscopy and calorimetric investigations of d-lyxose

Using broadband dielectric spectroscopy, we have studied different types of relaxation processes, namely, primary (α), secondary (β), and another sub-T_g process called γ-process, in the supercooled state of d-lyxose, over a wide frequency (10^-2–) and temperature range (120–340 K). In addition, the same sample was analyzed by differential scanning calorimeter. The temperature dependence of the relaxation times as well as the dielectric strength of different processes has been critically examined. It has been observed that the slower secondary relaxation (designated as β-) process shifts to lower frequencies with increasing applied pressure, but not the faster one. This pressure dependence indicates that the observed slower secondary relaxation (β-) is Johari–Goldstein relaxation process and faster one (γ-process) is probably the rotation of hydroxymethyl (–CH₂OH) side group attached to the sugar ring, that is, of intramolecular origin.     

Probing protein electrostatic interactions through temperature/reduction potential profiles

 The change in the equilibrium reduction potentials of the iron-sulfur proteins, Pyrococcus furiosus rubredoxin and P. furiosus ferredoxin, and heme protein, horse cytochrome c, has been calculated as a function of temperature using a numerical solution to the Poisson-Boltzman equation. Working curves for different internal dielectric constants were generated to best reproduce experimental observation. Based on a comparison of the experimental and simulated change in reduction potential with temperature, it is concluded that the dielectric constant of proteins is temperature-dependent and varies from protein to protein. For example, the temperature-dependent reduction potential of cytochrome c can only be simulated using a different temperature-dependent dielectric constant for each oxidation state, but this was not the case for rubredoxin or ferredoxin. The role of changes in ionization states of cytochrome c at alkaline pHs, where the reduction potential is known to be pH-dependent at room temperature, is also discussed in terms of electrostatic interaction energies as a function of temperature. It appears that temperature/reduction potential profiles may provide a direct method for measuring relative changes in internal protein dielectric constants. Received: 29 April 1996 / Accepted: 1 August 1996     

A dielectric analysis of liquid and glassy solid glucose/water solutions

Dielectric relaxation data covering a temperature range from above room temperature to below the glass transition for 40% (w/w) and 75% (w/w) glucose/water solutions in the frequency range between 5 and 13 MHz are presented. These data are used to obtain correlation times for the dielectric relaxation in the viscous liquid and the glass and are compared with correlation times determined from deuterium nuclear spin relaxation times [J. Chem. Phys., 110 (1999) 3472-3483]. The two sets of results have the same temperature dependence, but differ in magnitude by a factor of 3, implying that the relaxation is a small-step rotational diffusion. Both the structural relaxation (alpha process) and the slow beta process are present. In the 40% glucose/water sample, there is a dielectric relaxation attributable to the ice that forms at low temperature. It is shown that the reciprocal of the viscosity, the correlation time derived from the dielectric relaxation, and the dc conductivity have a similar dependence on temperature.